__________ weathering, the minerals in the rock change their chemical makeup.
During weathering, the minerals in the rock can undergo various chemical reactions that alter their composition. These reactions typically occur when the rock is exposed to water, oxygen, carbon dioxide, or acids present in the environment. Some common chemical changes that take place during weathering include dissolution, hydration, oxidation, reduction, hydrolysis, and carbonation.
- Dissolution: This process involves the dissolving of minerals in water. For example, when rainwater with dissolved carbon dioxide percolates through limestone, it can dissolve calcium carbonate, leading to the formation of caves and sinkholes.
- Hydration: Certain minerals, such as anhydrite, can absorb water molecules and form new hydrated minerals like gypsum. This process typically occurs in regions with high humidity.
- Oxidation: Oxygen in the atmosphere can react with iron-bearing minerals, causing them to oxidize and form new compounds. For instance, when iron-rich minerals like pyrite come into contact with oxygen and water, they can react to produce iron oxide minerals, giving rise to rust-colored stains on rocks.
- Reduction: In some cases, certain minerals may get reduced due to the absence of oxygen. For example, iron oxide minerals can be reduced in environments lacking oxygen, leading to the formation of iron sulfide minerals like pyrite.
- Hydrolysis: This process involves the reaction of minerals with water molecules, resulting in the breakdown of minerals and the formation of new clay minerals. Feldspar, a common mineral in many rocks, can undergo hydrolysis to form clay minerals like kaolinite.
- Carbonation: Carbon dioxide from the atmosphere can dissolve in rainwater, forming a weak carbonic acid solution. This acid can react with minerals like limestone or marble, leading to their gradual dissolution and the formation of calcium bicarbonate.
Overall, the chemical changes that occur during weathering can significantly affect the mineral composition and overall stability of rocks over time.